1. Field of the Invention
The present invention relates to a rotor for small motors, which permits ready junctioning of a commutator leg part to each commutator segment end and fitting and connection of a varistor, and a manufacturing method therefor.
2. Description of the Related Art
Connection of each commutator segment and a wound wire end according to the prior art will be described with reference to FIG. 5. FIG. 5 shows a schematic perspective view of the commutator unit of a small motor. In the drawing, reference numeral 11 denotes the shaft of a rotor; 22, a commutator segment; 24, a commutator core; and 26, a commutator leg part. Thus the commutator unit is composed of commutator segments 22 arranged over a resin-made commutator core 24 and commutator leg parts 26, each formed integrally with and at the end of a commutator segment 22 for connecting a wound wire end. FIG. 6 shows a profile of the commutator unit shown in FIG. 5 in a state of being coupled with a wound wire end. The commutator leg part 26, as illustrated, is caused to press down a wound wire end by being bent toward the commutator-segment, and is spot-welded.
FIG. 7 shows a varistor alone on its right part and the varistor in a fitted and connected state in the left part. In a small motor having a commutator, when a brush in sliding contact with the commutator passes between commutator segments, an arc is generated, and this arc may jam communication equipment or shorten the useful life of the brush. To solve these problems, fitting a varistor to the rotor of the motor as a spark suppressing element is a known art. An example of such varistor has the shape shown in the right part of FIG. 7. Its overall shape is a doughnut-like disk, and has as many electrodes as the magnetic poles of the rotor, i.e. as many as the commutator segments. Each electrode of this varistor 21 is soldered onto one or another of the commutator leg parts 26. This soldering not only electrically connects the varistor 21 but also is mechanically fixed concentrically with the commutator unit 20.
However, by this conventional connecting and fixing method, as oxidized film is formed over the commutator leg part 26 after wound wire ends are pressed down with the commutator leg part 26 and spot-welded, it is difficult to solder the varistor over them. Therefore, the oxidized film of the soldered portion of the commutator leg part has to be scraped off before the varistor is soldered.
The varistor connecting method according to the prior art also involves the problem of having to use a large quantity of solder because the varistor is mechanically fixed by bridging with solder as shown in FIG. 7.